This invention relates to a charge coupled imaging device comprising a semiconductor body having a surface with a matrix of elements for converting a radiation image into charge packets, arranged in a grid of lines and columns, and with a system of charge transport channels with which said charge packets are transported to a read-out register in a direction parallel to the columns under the control of clock voltages applied to clock electrodes, by which register the charge packets are transported line by line in a direction parallel to the lines of the grid to a read-out member, an electrode being present which extends transversely across the entire width of the matrix in the line direction and to which a voltage can be applied for dumping one or several lines, via a removal region, from between two lines which are read out via the read-out register. An electrode is a solid conductor by which a current can pass to or from another solid conductor.
Such an imaging device is known inter alia from European Patent Application EP 0 720 388 laid open to public inspection. An imaging device is described therein which can be operated in two different modes, i.e. in the xe2x80x9cstill image modexe2x80x9d and in the xe2x80x9cmotion preview modexe2x80x9d. In the first mode, all lines of the grid are read out and subsequently subjected to further signal processing so as to obtain the desired high resolution. In the second mode, which is used for displaying the captured image on an LCD of the viewfinder of the camera, only a limited number of lines is necessary, and the redundant lines present between the former lines are dumped into a removal region instead of being read out. The imaging device is of the interline type, with photodiodes arranged in a pattern of rows and columns and with charge transport channels between the columns of photodiodes. The charge packets formed in the photodiodes during an integration period are transported to a horizontal read-out register through these charge transport channels (which are screened against incident radiation). An FDG (fast dump gate) is provided between the vertical charge transport channels and the horizontal read-out register, by means of which FDG lines can be dumped in the xe2x80x9cmotion preview modexe2x80x9d. A disadvantage of this device is that a separate electrode and a separate voltage source for controlling the FDG are necessary for dumping the redundant lines.
The invention accordingly has for its object inter alia to provide a charge coupled imaging device in which redundant lines can be dumped without having the disadvantages described above.
Dumping of redundant lines may offer advantages also in types of imaging devices other than the imaging device described above. Thus, for example, the article xe2x80x9cA ⅔-in 1187 (H)xc3x97581(V) S-VHS-Compatible Frame-Transfer CCD for ESP and Movie modexe2x80x9d by Bosiers et al., published in IEEE Transactions on Electron Devices, Vol. 38, No.5, May 1991, pp. 1059/1068, describes an imaging device which comprises besides the photosensitive imaging section also a memory section adjoining the former and masked against incident radiation. The number of lines that can be stored in the memory section is 295, i.e. half the number of lines in the imaging section, which is 581. In the xe2x80x9cmovie modexe2x80x9d, the lines in the imaging section are added together in pairs to render it possible to store all charge generated in the imaging section in the memory section, so that the total number of lines in the imaging section is reduced by a factor 2 to fit the storage capacity of the memory section. Joining together of the lines achieves a high sensitivity. Often, however, an increase in the MTF (improved resolution) is considered more important, in which case it would be preferable to transport the lines from the imaging section alternately to the memory section and to the dump. The invention accordingly has for its object also to provide an imaging device of the frame transfer type which is provided with an imaging section and with a memory section smaller than the imaging section and which also offers the possibility of dumping redundant lines.
These and other objects, whether or not in combination with one another, are achieved in a charge coupled imaging device according to the invention which is characterized in that, the imaging device being built up from a photosensitive imaging section and a memory section screened against incident radiation and comprising a number of charge transport channels which are situated next to one another, which extend in the column direction, and which merge into the charge transport channels of the imaging section, said electrode for dumping the lines which are not used is situated at the transition between the imaging section and the memory section. Redundant lines are dumped at the transition between the imaging section and the memory section in an imaging device according to the invention. The entire frame of charge packets can be transported in the usual manner with 1-, 2-, 3-, or 4-phase clock voltages in the imaging section, while only those lines which are necessary for further processing are stored in the memory section.
Important advantages are obtained when the electrode with which lines are dumped is formed by a separate electrode which is controlled independently of the m-phase clock electrodes. A preferred embodiment which has the advantage that no separate electrode is necessary is characterized in that said electrode with which lines can be dumped comprises at least one clock electrode of the imaging section which is connected to other clock electrodes of the imaging section via clock lines. A further embodiment is characterized in that the charge transport channels of the imaging section and the memory section comprise electrodes which are connected to clock voltage means with which voltages can be applied whereby transport of charge packets takes place in the imaging section, while at the same time no transport of charge packets takes place in the memory section, and charge packets supplied via the imaging section are blocked by a potential barrier at the area of the memory section and are drained off through the removal region.
An important preferred embodiment, which, in a simple manner, prevents charge from lines to be dumped from partly joining charge packets of other lines during the process of dumping of lines, is characterized in that the removal region is provided with means for applying a voltage to the removal region for the purpose of dumping of charge packets, whereby at least locally a reduction of the potential barrier between the removal region and the charge transport channel is obtained as compared with the potential barrier obtaining during a preceding integration period.
The invention also relates to a method of operating a charge coupled imaging device comprising a semiconductor body which is provided at a surface with a matrix for converting a radiation image into charge packets, arranged in a grid of lines and columns, and with a system of charge transport channels with which said charge packets are transported in a direction parallel to the columns to a read-out register under the control of clock voltages applied to clock electrodes, which read-out register transports the charge packets line by line to a read-out member in a direction parallel to the lines of the grid, an electrode being present which extends in the line direction transversely across the width of the matrix and to which a voltage can be applied for dumping one or several lines via a removal region between two lines which are read out through the read-out register. Such a method according to the invention is characterized in that, an imaging device being used built up from a photosensitive imaging section and a memory section screened against incident radiation and comprising a number of charge transport channels which lie next to one another, which extend in the column direction, and which merge into the charge transport channels of the imaging section, one or several clock electrodes of the charge transport channels is/are used so as to form said electrode for dumping of lines which are not used, which electrode or electrodes is/are situated at the transition between the imaging section and the memory section.
A preferred method in which aliasing is suppressed at least partly, is characterized in that only one line out of every group of k lines formed in an integration period is stored in the memory section, the lines being shifted during the integration period such that said one line also contains electric charge generated at the areas of the other lines of said group of k lines.